The field of the present invention is in oil/gas suspension struts for off-road vehicles.
For ages men have been suspending a frame on which a load is to be carried from the axle of a wheel or wheels. At first the frame merely set on the axle, sort of like a wheelbarrow. However, the operator of the vehicles kept looking for more comfort to the operator and better suspension system to prevent damage to the vehicle. At first the frame was supported only by springs. The springs could be leaf springs or coil springs. Later on compressed gas was widely used as the spring element in suspension systems. The unrestrained or undampened motion of any spring element, either a mechanical or gas spring provides an unacceptable ride. Hence, the incorporation of dampening on shock absorber elements in any suspension system becomes common place. The shock absorbers include telescoping piston with a housing and the passage of fluid from one side of the piston to the other is controlled to give proper dampening to the vehicle.
In some of the heavy duty off-road vehicles each wheel may have a gas/oil suspension system. In this there is a housing having a piston therein and which has a gas, usually nitrogen in the upper end charged to a certain pressure and in contact with oil. The compressed gas acts as a spring and controlling the flow of oil from one portion of the system to another provides the dampening. In these vehicles it is most difficult to get the right combination of gas and oil with proper pressure and volume to obtain the desired spring rate over a wide range of loads. For example, if the right combination is found to give a smooth ride at no load on the vehicle then when the vehicle is completely loaded it might be too stiff a ride. Another problem which the prior suspension system has is that when the vehicle goes to rough or rolling terrain, frequently the four wheels are not on one plane. With the prior art suspension system the frames will be twisted by this uneven surface.
It is therefore an object of this present invention to provide a suspension system in which a dual spring rate can be obtained. It is still a further object of this invention to provide equalizing means between the two suspension systems so as to maintain the supported frame in a flat condition or single plane by preventing twisting forces from being applied to it.